1. Field of the Invention
This invention pertains to novel polysaccharides and their use in latex compositions and processes, and more particularly to polysaccharides having alkyl-aryl hydrophobes, and improved processes for their production in which polysaccharides provide latex compositions with improved rheology and stability.
2. Description of Background Information
Latex compositions typically have additives which modify the rheology or stability of the composition. Polysaccharides, and in particular cellulosics, have been described as additives to latex compositions for various purposes, including as protective colloids, thickeners, stabilizers or other rheology modifiers. For example, U.S. Pat. No. 4,684,704 (Craig) describes latex compositions containing hydrophobically modified, hydroxyethyl cellulose as a protective colloid. U.S. Pat. No. 4,243,802 (Landoll) and U.S. Pat. No. 4,352,916 (Landoll) describe the use of hydrophobically modified, hydroxyethyl cellulose as thickeners, emulsifiers and stabilizers for latex compositions. U.S. patent application Ser. No. 172,432, filed Mar. 24, 1988, entitled xe2x80x9cPREPARATION OF AQUEOUS POLYMER EMULSIONS IN THE PRESENCE OF HYDROPHOBICALLY MODIFIED HYDROXYETHYL CELLULOSExe2x80x9d, describes emulsion polymerization processes using hydrophobically modified hydroxyethyl cellulose, including alkyl-aryl-substituted materials.
Polysaccharides having aryl substituents are known. For instance, U.S. Pat. No. 1,451,331 (Dreyfus), U.S. Pat. No. 1,502,379 (Dreyfus), U.S. Pat. No. 1,589,607 (Lilienfeld), and U.S. Pat. No. 1,972,135 (Dreyfus) describe hydroxyethyl cellulose with aralkyl, e.g. benzyl, substitution. Japanese Patent Application Publication No. 82-28003 (Nakamura) describes benzyl substituted, quaternary nitrogen-containing cellulosics in cosmetics. U.S. Pat. No. 4,663,159 (Brode, II et al.) describes water-soluble, cationic polysaccharides containing hydrophobes including aralkyl or alkaryl substituents, having various utilities.
This invention pertains to polysaccharides with alkyl-aryl hydrophobes and to latex compositions and processes using such polysaccharides. The latex composition contains water, latex polymer and water-soluble polysaccharide having alkyl-aryl hydrophobes. A process for improving the rheology of latex compositions is provided using such polysaccharides. Processes for producing these polysaccharides are also provided. One process comprises reacting a polysaccharide ether with an alkyl-aryl hydrophobe containing compound wherein the ether substitution on the polysaccharide provides an increase in the amount of hydrophobe substitution reacted onto the polysaccharide. Another process comprises reacting a polysaccharide with an alkyl-aryl, hydrophobe-containing glycidyl ether compound.
Polysaccharides are generally high molecular weight polymers composed of monosaccharide repeating units joined by glycosidic bonds. Alkyl-aryl hydrophobe substitution of polysaccharides are polysaccharides which have one or more alkyl-aryl substituents, with at least about 10, preferably from about 12 to about 24, and most preferably from about 15 to about 18, carbon atoms in the alkyl-aryl group, i.e. hydrophobe. The aryl portion of the hydrophobe may have one or more aryl rings, which may be fused, carbocyclic or heterocyclic, unsubstituted or substituted with other functional groups, such as halogen, nitro, hydroxyl, amino or other substituents. The alkyl portion of the hydrophobe may be straight or branched chain, cyclic or acyclic, saturated or partially unsaturated, unsubstituted or substituted with other functional groups, such as halogen, hydroxyl or other substituents. Alkyl-aryl hydrophobes include both aralkyl or alkaryl groups. Typical hydrophobes include, but are not limited to, one or more of the following: alkaryl such as t-butylphenyl, nonylphenyl or dodecylphenyl; and aralkyl such as phenylhexyl or naphthyldodecyl. Preferred hydrophobes are nonylphenyl and dodecylphenyl.
The degree of hydrophobe substitution, i.e. DS, defined as the average moles of hydrophobe substituent per mole of polysaccharide repeat unit, may vary depending upon the presence of other substituents, type of hydrophobe and type of polysaccharide. Generally, the DS of the hydrophobe is greater than zero, preferably from 0.001 to about 0.1, and most preferably from 0.005 to about 0.03.
The polysaccharides with alkyl-aryl hydrophobes include polymers of repeating units represented by the structural formula: 
In Formula I, for each repeating unit individually: 
herein R4 is 
or a mixture of hydrogen and 
is the residue of a polysaccharide repeat unit and may include additional reactive groups, as in xanthan gum;
x is from about 50 to about 20,000;
each y1, y2 and y3 is 0 or 1;
each Z1, Z2 and Z3 is a divalent connecting segment; and
each R1, R2 and R3 is individually a hydrogen, an unsubstituted or a nitrogen-, oxygen-, sulfur- or carboxyl-containing hydrocarbyl group or Rh, wherein Rh is an alkyl-aryl hydrophobe, provided that (1) when R1, R2 or R3 is hydrogen then y1, y2 or y3, respectively is 0 and (2) one or more repeating units have one or more R1, R2 or R3 which is Rh.
In Formula I, Q is preferably oxygen providing anhydroglucose repeat units, and most preferably cellulose. The number of repeat units, defined by x, is preferably from about 50 to about 20,000 and most preferably from about 250 to about 4,000, providing a molecular weight of from several thousand up to several million. The molecular weight of the polysaccharide may be varied using well established procedures, such as controlled degradation.
In Formula I, the ether substituents, i.e. (Z1)y1xe2x80x94R1, (Z2)y2xe2x80x94R2 and (Z3)y3xe2x80x94R3, are usually hydrogen with some alkyl-aryl hydrophobes, and preferably hydroxyethyl, present. Since only one or more repeating units must have one or more Rh, not every polysaccharide repeat unit must have an alkyl-aryl hydrophobe. Generally, only a minor portion of repeat units will have one or more hydrophobes. Typical ether substituents include, but are not limited to, one or more of the following: hydrogen, i.e. xe2x80x94H; unsubstituted hydrocarbyl such as xe2x80x94CH3, xe2x80x94CH2CH3, xe2x80x94CH2C6H5, or xe2x80x94C16H33; nitrogen-, oxygen-, sulfur- or carboxyl-containing hydrocarbyl such as xe2x80x94CH2CH2OH; xe2x80x94CH2COOH; xe2x80x94CH2COOxe2x88x92Na+ or 
hydrophobes with or without connecting segments, including the alkyl-aryl hydrophobes described previously, such as 
Preferably the ether substituents also include hydroxyethyl, i.e. xe2x80x94CH2CH2OH, in an amount sufficient to provide water solubility.
In Formula I, the divalent connecting segment, represented by Z1, Z2 and Z3, designates the portion of the ether substituent which is provided between the cellulose ether oxygen, or Q group, and the main portion of the substitutent, such as an alkyl-aryl group. When R1, R2 or R3 is hydrogen, i.e. when the group represented is an unsubstituted hydroxyl, there is no connecting segment and y1, y2 or y3 is correspondingly 0. When R1, R2 or R3 is not hydrogen, then a connecting segment may or may not be provided. Generally, the connecting segment represents the residual portion of the compound used to provide an alkyl-aryl substitutent on the polysaccharide, which portion is not the alkyl-aryl group per se. Typical connecting segments, when present, include, but are not limited to: unsubstituted or hydroxy-substituted alkyl or alkoxy groups such as methylene, i.e. xe2x80x94CH2xe2x80x94, ethoxy, i.e. xe2x80x94CH2CH2Oxe2x80x94, or glycidyl ethers, i.e. 
Preferably, the connecting segment is absent or present as xe2x80x94CH2xe2x80x94 or most preferably as 
The polysaccharide may contain additional substitution, i.e. other than the hydrophobes, such as may be required to provide the requisite water solubility or other properties. The other substituents may be ionic or nonionic providing nonionic, cationic, anionic or amphoteric polysaccharide. Typical additional substituents include, but are not limited to, one or more of the ether substituents described previously. The amount of additional substitution, i.e. molar substitution defined as the average moles of such substituent per mole of polysaccharide repeat unit, designated MS, is not critical but may be any amount desired. Preferably, the polysaccharide will have a hydroxyethyl MS sufficient to provide water solubility, if needed, and/or improved enzyme reistance if desired. Hydroxyethyl MS may generally be from about 1.5 to about 6, and preferably from about 3 to about 5.
The hydrophobe-substituted polysaccharides can be produced from readily available polysaccharide starting materials. These materials include naturally occurring, biosynthesized and derivatized carbohydrate polymers or mixtures thereof. The type of polysaccharide is not critical and includes the entire starch and cellulose families; pectin; chitosan; chitin; the seaweed products such as agar and carrageenan; alginate; the natural gums such as guar, arabic, and tragacanth; bio-derived gums such as dextran and xanthan; and other known polysaccharides. Preferred polysaccharides are cellulosics, including cellulose ethers, which may be derived from conventional materials, such as chemical cotton, cotton linters, wood pulp, alkali cellulose, as well as ether derivatives of these materials.
Cellulose ethers which may be used include, but are not limited to, one or more of the following: hydroxyethyl cellulose; hydroxypropyl cellulose; methyl cellulose; carboxymethyl cellulose; carboxyethyl cellulose; hydroxypropyl ethyl cellulose; hydroxyethyl carboxymethyl cellulose; and the like. A particularly preferred polysaccharide is hydroxyethyl cellulose.
Any reaction condition sufficient to modify the polysaccharide with the hydrophobes may be used, including well established etherification procedures, such as described in U.S. Pat. No. 4,663,159 (Brode, II, et al.) or U.S. Pat. No. 4,228,277 (Landoll). This reaction may be conducted using any compound having the hydrophobe and a functional group which reacts with the polysaccharide. Typical functional groups include, but are not limited to, one or more of the following: halides, such as chlorides or bromides; oxiranes, such as epoxides including glycidol and its esters; acids, including esters, acid halides or salts thereof, such as carboxylic acids or sulfates; (thio)isocyanates; and halohydrins. Alkyl-aryl halides may be used but may not be desirable due to problems with corrosivity and having to remove halides from the product. Preferably a glycidyl ether, such as nonyl- or dodecylphenyl glycidyl ether, is used.
The hydrophobe substitution reaction may be conducted at any desired temperature, typically between 20xc2x0 C. to 125xc2x0 C. and preferably from about 55xc2x0 C. to about 95xc2x0 C., for a time sufficient to provide the desired amount of substituents, typically from about 0.5 hour to about 12 hours or more and preferably from about 1 to 6 hours. The reaction may be conducted with diluent, solvent or catalyst as desired and is typically done in an inert medium in the presence of a caustic catalyst, such as an alkali metal hydroxide or the like material.
In a preferred embodiment, the hydrophobe substitution is conducted by reacting a compound, having an alkyl-aryl group with a polysaccharide ether containing another substituent, such as hydroxyethyl, in an amount which increases the efficiency of hydrophobe substitution. The MS of other ether substitution, i.e. MSE, may vary depending upon the types of polysaccharide, hydrophobe and other ether substituents present and is generally at least that amount which provides increased hydrophobe substitution as compared to an MSE of 0. In embodiments when the polysaccharide is cellulose and the other ether substituent is hydroxyethyl, MSE may range from greater than 0, preferably from about 1.5 to about 6 and most preferably from about 3.5 to about 5 average moles of other ether substituent per mole of polysaccharide repeat unit.
In another preferred embodiment, the hydrophobe substitution is conducted using an alkyl-aryl compound having a functional group which is a glycidyl ether. Such compounds may be represented by the structural formula: 
wherein Rh is an alkyl-aryl hydrophobe as defined previously, in Formula I. Substitutions using such compounds have been found to provide higher reaction efficiencies when compared to other functional groups, including the closely related, corresponding epoxides, such as represented by the structural formula: 
wherein Rh is as previously defined. While not bound to any particular theory, the increased reaction efficiencies provided by alkyl-aryl glycidyl ethers may be due to higher reactivity of glycidyl ether groups to nucleophilic attack by the polysaccharide. Consequently, increased reaction efficiencies may be exhibited by other glycidyl ethers, including linear or branched alkyl glycidy, ethers, such as hexadecyl glycidyl ether, as compared to the corresponding alkyl epoxides, such as 1,2-epoxyhexadecane.
In a typical procedure the hydrophobe substitution reaction is carried out in a slurry of the desired polysaccharide in an appropriate aqueous diluent system. Suitable diluents include, but are not limited to, isopropyl alcohol, t-butyl alcohol, sec-butyl alcohol, propyl alcohol, ethanol, methanol, methylethylketone, water, tetrahydrofuran, dioxane, 2-butoxyethanol, 2-ethoxyethanol, acetone, and mixtures of these materials. Suitable weight ratios of diluent to polysaccharide are in the range of about 4:1 to 25:1. Because the reaction is generally carried out heterogeneously, it is important that the diluent system normally not be a solvent for either the starting polysaccharide or the hydrophobe-modified product.
The polysaccharide may be causticized with a suitable caustic catalyst such as sodium hydroxide, potassium hydroxide or lithium hydroxide, with sodium hydroxide being preferred. The molar ratio of caustic to polysaccharide may suitably vary between 0.4 to 2.0. Many polysaccharides that are in contact with any base may be readily degraded by oxygen. It is accordingly necessary to exclude oxygen from the reaction vessel during the time in which caustic is present. It is suitable to carry out the reaction under an inert gas such as nitrogen.
After being causticized with a suitable amount of caustic catalyst, the hydrophobic reactant may be added, and the reaction is conducted at a suitable temperature for a time sufficient to provide the desired amount of substitution. Alternately, the polysaccharide may be first reacted with one or more appropriate electrophiles to render the polysaccharide water soluble followed by a sequential reaction with the hydrophobic reactant, or the polysaccharide may be simultaneously reacted with one or more electrophiles and the hydrophobic reactant. Suitable electrophiles include ethylene oxide, propylene oxide, chloroacetic acid and its salts, 1,3-propane sultone, methyl chloride, ethyl chloride, glycidol, 3-chloro-1,2-propanediol, and 2-chloroethanol.
Latex compositions can be provided having as essential components: water; latex polymer; and the polysaccharide. The kind and amount of latex polymer is not critical, and may be provided based on well established procedures. Typical latex polymers include, but are not limited to, various types such as the following: acrylics; alkyds; celluloses; coumarone-indenes; epoxys; esters; hydrocarbons; maleics; melamines; natural resins; oleo resins; phenolics; polyamides; polyesters; rosins; silicones; styrenes; terpenes; ureas; urethanes; vinyls; and the like. Illustrative latex polymers include, but are not limited to, one or more homo- or copolymers containing one or more of the following monomers: (meth)acrylates; vinyl acetate; styrene; ethylene; vinyl chloride; butadiene; vinylidene chloride; vinyl versatate; vinyl propionate; t-butyl acrylate; acrylonitrile; neoprene; maleates; fumarates; and the like, including plastisized or other derivatives thereof.
The amount of polysaccharide which may be used in the latex composition is not narrowly critical. In the broadest sense, the amount of polysaccharide is that which is an effective amount in providing improved rheology or stability to the latex composition. Typically, the amount of polysaccharide is at least about 0.05, preferably from about 0.15 to about 3, and most preferably from about 0.25 to about 1.5 weight percent of the latex composition.
The amount of latex polymer used in the latex composition is not critical, but may be any amount following well established procedures using latex polymers. Typically, the amount of dry latex polymer is at least about 1, preferably from about 2 to about 50, and most preferably from about 3 to about 40 weight percent of the total latex composition.
The latex composition may optionally contain other components such as those generally used in latex compositions. Typical components include, but are not limited to, one or more of the following: solvents such as aliphatic or aromatic hydrocarbons, alcohols, esters, ketones, glycols, glycol ethers, nitroparaffins or the like; pigments; fillers, dryers; flatting agents; plastisizers; stabilizers; dispersants; surfactants; viscosifiers including polymeric associative thickeners, polysaccharide-based thickeners and so on; suspension agents; flow control agents; defoamers; anti-skinning agents; preservatives; extenders; filming aids; crosslinkers; surface improvers; corrosion inhibitors; and other ingredients useful in latex compositions.
Processes for producing latex compositions having improved rheology and stability can be provided by combining the latex polymer and polysaccharide with water following established procedures.
Although not bound by any particular theory it is believed that the polysaccharides control the rheology of the latex composition by two mechanisms. As with other cellulosics, the aqueous phase of the composition is thickened by the presence of a large hydrodynamic volume resulting from the relatively high molecular weight and water of hydration surrounding the polysaccharide. The alkyl-aryl substitution also thickens the latex composition by an associative mechanism wherein the hydrophobes interact with each other and hydrophobic portions of the latex polymer or other ingredients present resulting in improved properties such as high viscosity at low shear, improved spatter resistance and improved flow and leveling, while avoiding problems with syneresis, color acceptance, color development and viscosity stability.
Latex compositions and processes using the polysaccharides are provided whereby the polysaccharide may be used as a protective colloid, thickener, stabilizer or other rheology modifier, such as for emulsion polymerization.
The polysaccharide may also be used in a variety of applications other than in latex compositions and processes. Additional applications include, but are not limited to: cosmetics, such as shampoos; biomedicine such as in oral care including toothpaste or in pharmaceuticals including timed- or controlled-release formulations; detergents such as in laundry or surface cleaners; various other timed-release applications including pesticides; and other areas in which a protective colloid, stabilizer, thickener or rheology modifier is desired.